1. Field of the Invention
The present invention relates to a magnetoresistance effect device which causes a substantial magnetoresistance change with a low magnetic field, a magnetoresistance head incorporating the same which is suitable for use in high density magnetic recording and reproduction, and a method for producing a magnstoresistance effect device.
2. Description of the Related Art
A magnetoresistance sensor (hereinafter, referred to simply as an xe2x80x9cMR sensorxe2x80x9d) and a magnetoresistance head (hereinafter, referred to simply as an xe2x80x9cMR headxe2x80x9d) employing a magnetoresistance effect device (hereinafter, referred to simply as an xe2x80x9cMR devicexe2x80x9d) have been developed and used in practice. For a magnetic body in the MR device, typically, an Ni0.8Fe0.2 parmalloy film or an Ni0.8Co0.2 alloy film is used. When using such a magnetoresistance effect material, the resulting magnetoresistance rate of change (hereinafter, referred to simply as an xe2x80x9cMR ratioxe2x80x9d) is about 2%. A larger MR ratio has been desired for an MR device with a higher sensitivity. Recently, it has been found that an [Fe/Cr] or [Co/Ru] artificial grating film which is antiferromagnetically connected via a metallic, non-magnetic thin film such as a Cr film or an Ru film exhibits a large resistance change of substantially 100% (giant magnetoresistance effect) under a strong magnetic field (about 1 to 10 kOe) (Physical Review Letter, Vol. 61, p. 2472 (1988); Physical Review Letter, Vol. 64, p. 2304 (1990)). However, such an artificial grating film requires a strong magnetic field of several kOe to several tens of koe to obtain a large MR change, and thus is not very practical for use in a magnetic head, or the like.
A spin valve type film where an antiferromagnetic material, Fexe2x80x94Mn, is attached to Nixe2x80x94Fe/Cu/Nixe2x80x94Fe has also been proposed (Journal of Magnetism and Magnetic Materials 93, p. 101, (1991)), which is capable of operating under a slight magnetic field. In such a spin valve film, a ferromagnetic film (pin layer) in contact with the ferromagnetic material is provided with a unidirectional anisotropy through an exchange connection, whereby the magnetization direction of the ferromagnetic film is fixed in a certain direction. On the other hand, the magnetization direction of the ferromagnetic layer (free layer), which is provided via the pin layer and a non-magnetic layer, can be changed relatively freely in response to an external signal magnetic field. Therefore, the respective magnetization directions of the pin layer and the free layer change with respect to each other, thereby varying the electric resistance. The necessary operating magnetic field of such an MR material is small, and, the linearity thereof is also good. However, the MR ratio of such an MR material is as low as about 2%, and the Fexe2x80x94Mn film has a poor corrosion resistance. Moreover, since the Neel temperature of the Fexe2x80x94Mn film is low, the device characteristics are substantially dependent upon temperature.
It has been proposed to use an oxide antiferromagnetic body such as NiO (Nihon Oyo Jiki Gakkaishi 18, p. 355 (1994)) or xcex1-Fe2O3 (Japanese Laid-open Publication Nos. 8-279117 and 9-92904) as the antiferromagnetic body used in a spin valve film. A spin valve film employing an NiO film has an MR ratio of about 4% to 5% which is greater than that of a spin valve film employing Fexe2x80x94Mn. However, such a spin valve film has not been used in practice since it is difficult to produce, and the heat stability of an exchange bias magnetic field thereof is poor. In the case of a spin valve film employing xcex1-Fe2O3, the unidirectional anisotropy in the pin layer is weak, and the coercive force thereof is large. Therefore, such a spin valve film is likely to be a coercive force difference type spin valve film. Moreover, a sufficient MR ratio cannot be obtained unless the film is subjected to a heat treatment after the deposition.
Another type of spin valve having a structure such as Nixe2x80x94Fe/Cu/Coxe2x80x94Pt and utilizing the coercive force difference between a hard magnetic film and a soft magnetic film has also been proposed, where a hard magnetic material (e.g., Coxe2x80x94Pt) is used in place of the antiferromagnetic material. In such a case, magnetization parallelism or magnetization antiparallelism is created by rotating the magnetization direction of the soft magnetic film (Nixe2x80x94Fe film) by using a coercive force less than that required for a hard magnetic film. However, this type of spin valve has not been used in practice, since it is difficult to improve the characteristics of the soft magnetic layer.
As described above, the conventional spin valve type MR device does not have a sufficient MR ratio. The conventional spin valve employing NiO provides a high MR ratio, but has problems such as a poor heat stability, a undesirable hysteresis of the MR curve, and an insufficient pinning magnetic field. In the case of the other conventional spin valve film xcex1-Fe2O3, the MR ratio is lower than that of the spin valve film employing Nio, and a sufficient MR ratio cannot be obtained unless the film is subjected to a heat treatment after the deposition.
According to one aspect of this invention, a magnetoresistance effect device of the present invention includes a multilayer film. The multilayer film includes an antiferromagnetic film, a first ferromagnetic film, a non-magnetic film and a second ferromagnetic film, which are provided in this order on a non-magnetic substrate directly or via an underlying layer. The antiferromagnetic film includes an xcex1-Fe2O3 film. A surface roughness of the multilayer film is about 0.5 nm or less.
In one embodiment of the invention, 2, the first ferromagnetic film includes a Co1xe2x88x92xFex alloy film (0 less than xxe2x89xa60.5, where x denotes an atomic composition ratio).
In one embodiment of the invention, the first ferromagnetic film is formed by providing a Co1xe2x88x92xFex alloy layer (0 less than xxe2x89xa60.5, where x denotes an atomic composition ratio) on an Nixe2x80x94Fe alloy layer or an Nixe2x80x94Fexe2x80x94Co alloy layer.
In one embodiment of the invention, a main component of the underlying layer is Pt or Au.
In one embodiment of the invention, a thickness of the xcex1-Fe2O3 film is in a range between about 5 nm and about 40 nm.
In one embodiment of the invention, an easy axis of the second ferromagnetic film is arranged so as to be substantially. perpendicular to a direction of a signal magnetic field to be detected.
According to another aspect of this invention, a magnetoresistance effect device includes a multilayer film. The multilayer film includes an antiferromagnetic film, a first ferromagnetic film, a non-magnetic film and a second ferromagnetic film, which are provided in this order on a non-magnetic substrate directly or via an underlying layer. The antiferromagnetic film includes a layered structure including an xcex1-Fe2O3 film and a second antiferromagnetic film.
In one embodiment of the invention, the second antiferromagnetic film includes an NiO film or a CoO film.
In one embodiment of the invention, the second antiferromagnetic film is overlying the xcex1-Fez2O3 film
In one embodiment of the invention, the xcex1-Fe2O3 film is overlying the NiO film.
In one embodiment of the invention, an easy axis of the second ferromagnetic film is arranged so as to be substantially perpendicular to a direction of a signal magnetic field to be detected.
According to still another aspect of this invention a magnetoresistance effect device includes a multilayer film. The multilayer film includes an antiferromagnetic film, a first ferromagnetic film, a non-magnetic film and a second ferromagnetic film, which are provided in this order on a non-magnetic substrate directly or via an underlying layer. The antiferromagnetic film includes an xcex1-Fe2O3 film. A thickness of the xcex1-Fe2O3 film is in a range between about 5 nm and about 40 nm.
In one embodiment of the invention, an easy axis of the second ferromagnetic film is arranged so as to be substantially perpendicular to a direction of a signal magnetic field to be detected.
According to still another aspect of this invention, a magnetoresistance effect device includes a multilayer film. The multilayer film includes a first antiferromagnetic film, a first ferromagnetic film, a first non-magnetic film, a second ferromagnetic film, a second non-magnetic film, a third ferromagnetic film and a second antiferromagnetic film, which are provided in this order on a non-magnetic substrate directly or via an underlying layer. The first antiferromagnetic film includes an xcex1-Fe2O3 film. A surface roughness of the multilayer film is about 0.5 nm or less.
In one embodiment of the invention, an easy axis of the second ferromagnetic film is arranged so as to be substantially perpendicular to a direction of a signal magnetic field to be detected.
According to still another aspect of this invention a magnetoresistance effect device includes a multilayer film. The multilayer film includes a first antiferromagnetic film, a first ferromagnetic film, a first non-magnetic film, a second ferromagnetic film, a second non-magnetic film, a third ferromagnetic film and a second antiferromagnetic film, which are provided in this order on a non-magnetic substrate directly or via an underlying layer. The first antiferromagnetic film includes a layered structure including an xcex1-Fe2O3 film and a third antiferromagnetic film.
In one embodiment of the invention, the second antiferromagnetic includes an Irxe2x80x94Mn film.
In one embodiment of the invention, an easy axis of the second ferromagnetic film is arranged so as to be substantially perpendicular to a direction of a signal magnetic field to be detected.
In one embodiment of the invention, at least one of the first ferromagnetic film and the third ferromagnetic film includes an indirect exchange coupling film.
According to still another aspect of this invention, a magnetoresistance effect device includes a multilayer film. The multilayer film includes an anti-ferromagnetic film, an indirect exchange coupling film, a first non-magnetic film, a first ferromagnetic film, which are provided in this order on a non-magnetic substrate directly or via an underlying layer. The anti-ferromagnetic film includes an xcex1-Fe2O3 film. The indirect exchange coupling film includes a second non-magnetic film and a pair of second ferromagnetic films interposing the second non-magnetic film therebetween.
In one embodiment of the invention, a main component of the second ferromagnetic film is Co.
In one embodiment of the invention, a main component of the second non-magnetic film is Ru
According to still another aspect of this invention, a magnetoresistance head includes: a magnetoresistance effect device as described above; and a shield gap section for insulating the magnetoresistance effect device from a shield section.
According to still another aspect of this invention, a method for producing a magnetoresistance effect device is provided. The device includes a multilayer film, the multilayer film includes an antiferromagnetic film, a first ferromagnetic film, a non-magnetic film and a second ferromagnetic film, which are provided in this order on a non-magnetic substrate directly or via an underlying layer. The method includes: a first step of forming the antiferromagnetic film having a thickness in a range between about 5 nm and about 40 nm on the non-magnetic substrate directly or via the underlying layer; and a second step of depositing, on the antiferromagnetic film, the first ferromagnetic film, the non-magnetic film and the second ferromagnetic film in this order so that a surface roughness of the multilayer film is about 0.5 nm or less. The first step includes a step of sputtering a target whose main component is xcex1-Fe2O3.
According to still another aspect of this invention a method for producing a magnetoresistance effect device is provided. The device includes a multilayer film, the multilayer film includes a first antiferromagnetic film, a first ferromagnetic film, a first non-magnetic film, a second ferromagnetic film, a second non-magnetic film, a third ferromagnetic film and a second antiferromagnetic film, which are provided in this order on a non-magnetic substrate directly or via an underlying layer. The method includes: a first step of forming the first antiferromagnetic film on the non-magnetic substrate directly or via the underlying layer; a second step of depositing, on the antiferromagnetic film, the first ferromagnetic film, the first non-magnetic film, the second ferromagnetic film, the second non-magnetic film, the third ferromagnetic film and the second anti-ferromagnetic film in this order so that a surface roughness of the multilayer film is about 0.5 nm or less. The first step a step of sputtering a target whose main component is xcex1-Fe2O3.
Thus, the invention described herein makes possible the advantages of: (1) providing an MR device which exhibits a large MR ratio by using an xcex1-Fe2O3 film or an xcex1-Fe2O3/NiO layered film so as to precisely control the surface roughness of the interface; (2) providing a method for producing such an MR device; and (3) providing an MR head incorporating such an MR device.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.